This invention relates to the art of electroplating palladium and its alloys. Numerous plating baths have been proposed for this purpose. Typical baths are taught, for example, in U.S. Pat. Nos. 1,921,941; 3,150,065; 3,162,512; 3,206,382; 3,458,409; 3,530,050; 3,544,345; 3,637,474; and 3,933,602. The foregoing patents discuss systems containing, for example, palladium di- and tetrammine halides, palladium-urea sulfite complexes, palladium dinitrile complexes, palladium tetrammine nitrate or sulfate complexes and palladium amine sulfite complexes. The possible use of an alkylene diamine phosphonate derivative in conjunction with a palladium sulfite complex has been suggested, for example, in the last above mentioned patent.
It would be desired to have available an electroplating bath which, when employed for the deposition of pure palladium, would yield a deposit which may be subsequently cold formed without destroying the integrity of the electrodeposited coating. The coating must continue to exhibit acceptable low porosity and good adhesion even after cold forming. Toward this end it is desired that the bath be resistant to hydrogen formation since hydrogen generated would be adsorbed by the palladium deposit embrittling the deposit and thereby degrading the post-formability of the palladium coating. It would also be desirable to have available in the art a palladium electroplating bath which may be employed for deposition on iron, cobalt or nickel substrates which are normally passivated under alkaline conditions.